IBM's "PS/2" VGA color monitors, models 8512 and 8513, have had
frequent maintenance problems. There are at least two different
models of each monitor. They are manufactured in Korea, probably
by Samsung or Tatung.

Schematic diagrams are apparently unavailable. The following is a
summary of many frustrating hours at the repair bench:

The top of the 8512 or 8513 case is fastened either by two internal
plastic clips (see below), or "tamperproof" Torx T-20 screws with
center pins. The Torx driver must have a long, slender shaft
(preferably magnetic) to reach the screw heads.

S/N 23-xxxxx: Plastic clips hold top front of case. The internal
catches can be released by inserting a pair of special tools made of
sheet-metal, shaped approximately like:

The angle at the end is more acute (25 degrees) than shown in
this ASCII diagram.

Alternatively, insert long, thin screwdriver into rectangular holes
and push clips downward. An Apple Macintosh case-separation tool
is sometimes useful to help remove back the cover. It is best to
release both clips simultaneously.

NOTE: Cut the silicone glue at the CRT base and unplug the tube before
working on the main board! The glass neck is easily broken. A
monitor with broken CRT is not economically repairable. The voice of
experience speaks. :-)

Symptom: No power or intermittent power:

Some models (including those whose serial numbers begin with 23) have
the AC power connector soldered directly to the main circuit board.
The wave-soldered connections are too thin for heavy components or
those subject to flexure: They crack, opening the circuit. Resolder
them, using lots of solder. Also use a magnifying lens to inspect the
solder joints of the flyback transformer, the deflection-yoke
connector and (rarely) the CRT socket. These often fail in the same
manner as the power connector. I always resolder all the
above-mentioned connections on general principle.

Failed component: Vertical amplifier (large IC attached to heat sink;
TDA-1670A manufactured by SGS, whose quality control is infamous).
People at IBM have told us that this chip is a weak point. Use heat-
sink compound when installing new IC. The replacement IC may last
indefinitely, or may fail in a few days. Sylvania's ECG 1862 is a
replacement for TDA1670A.

When the IC fails, a 2.2 ohm 1/4-watt resistor in series with its
power supply lead (diode and capacitor leading to a flyback pin) burns
beyond recognition. This resistor is used as a fuse. The value is
not critical (may be up to 20 ohms) but be sure the replacement
resistor is a metal-film type which burns quiescently, instead of a
carbon resistor which will start a fire. Leave the resistor leads
long, mounting the resistor one inch [2cm] mabove the circuit board.

Before replacing IC, inspect for cracked solder connections on the
male deflection-yoke connector (mounted on the main circuit board).

Also check C309 (2200uf 16v). If C309 is bad, the new amplifier may
fail immediately or in a few days.

Symptoms: Power Supply Problem:

Immediate power supply shutdown.

Power supply shutdown/restart about once per second.

Squeal from power supply, wavy left and right edges of
picture; may become normal after warmup.

Bad component: C120 (10 uf 35v). This capacitor is common to most
models of 8512/8513, and has the same identifying number on their
circuit boards. It is located near the front of the power supply
area, in the corner with the green LED pilot light, sometimes near a
large green resistor. Replace this capacitor on general principle
anytime you open an 8512 or 8513. This capacitor fails from heat;
dissection of bad capacitors reveals no moisture within. The
replacement should have a temperature rating of 105 deg. C. (typified
by end plug made of epoxy instead of rubber). Heat-induced capacitor
failure is a common problem in switching power-supplies. If high-
temp. capacitors are unavailable, leave the leads long so that the new
capacitor can be placed further from the abovementioned resistor which
gets hot enough to discolor the circuit board and adjacent plastic
standoff.

If capacitor is good, check diode CR105. This diode sometimes has
thermal problems resulting in intermittent or permanent short, causing
symptoms as above. Replace with a fast-recovery diode such as 1N4937;
leave leads long for cooling. (We use 1N4937 as a generic replacement
for high-frequency rectifiers in monitors, both in switching power
supplies and flyback-derived voltage sources. Common rectifier diodes
such as 1N4004 will overheat when used at the frequencies of switching
power supplies or of flyback transformers.

Also check CR212, near the flyback transformer. It often shorts.
Rating is 3A, 600V.

If new thermistor is unavailable: Remove the shorted
device, use a handheld de-gaussing coil after the monitor has been
returned to its operating position.

Replacement thermistors are not available from IBM. A suitable
replacement for the thermistor in IBM 8512, 8513 and 3192 is the one
used in NEC 1401 monitors. It is NEC part number 38112026, "positive
thermistor degaussing control," $2.95 from:

NEC Home Electronics
1255 Michael Dr.
Wood Dale IL 60191-1094.

The NEC device is slightly larger and apparently more robust than the
original. On some types the middle leg must be bent to fit the
hole in the printed-circuit board.

(Rare): Blown fuse may result from shorted diodes which rectify 115
VAC power, or from shorted FET power-supply switching transistor.

Resolder broken connections on the "red cut" control (RV801 on
the CRT board). The manufacturer produced a large number of this
model with that device improperly installed. Re-balance colors
as necessary.

Symptom: No power, or power supply making squealing sound.
Exploded capacitors on CRT board or inside power supply:

Replace exploded capacitors (10 uf 100v) as required. Replace
C18, C21 and C22 in the power supply. Use high-temperature
types. Failure of these capacitors may cause the power supply's
regulation to fail, causing power filter and video decoupling
capacitors to explode. The power supply to the CRT board should
deliver aprox. 70 volts.

Problem: Bad video cable. Wires often break inside the connector.
There are several variations of the inner end of the cable. The
one most prone to failure is used on 8512 s/n 72-xxxxxxx. Its
IBM part number is 61X8888. It is also available from other
sources.

New connectors are available from electronics parts distributors, but
installing them is very difficult because the inner conductors of the
coaxial cables are small and brittle. We have spliced a few cables
recovered from junked monitors but that is a laborious process.

IBM agreed to replace some 8512 and 8513 monitors under certain
conditions: See IBM documents 8512 ECA026 and 8513 ECA017. The
replacement offer has long EXPIRED.

8512's: Serial number with "72" prefix, s/n between 72-0120000 AND
72-0405000: Display is out of focus and/or excessively bright.

8513's: Serial number with "72" prefix, s/n below 72-0640000:
Display out of focus.

Those series appear no less reliable than others. Some replacement
units were new, others are used/reworked and have new serial numbers
attached. These appear to have new flyback transformers. Some have
subsequently failed for other reasons.

Symptom: Out of focus (8513 s/n 72-...)

If the focus control on the flyback is turned to the end of its travel
and the display is still out of focus, replace the flyback.
Replacement type is TFB-185A. The replacement may appear to have two
controls instead of one; the control labeled SCREEN is a dummy (see
below).

Many of our 8512 and 8513 monitors have failed from long service:
Since they have integral power switches, and the screens are
black when the computer is turned off, users tend to leave them
on forever. Life will be significantly extended by turning them
off overnight and on weekends.

CRT focus degrades with age. If the picture will not focus
satisfactorily and the focus control is not at an extreme (see
above), repair is not economical unless you have a good tube
salvaged from a scrapped unit. Transplant the CRT and deflection
yoke together; if the yoke is disturbed, reconvergence of colors
is extremely difficult.

Symptom: Left and right edges of picture are curved inward
(pincushion distortion); internal adjustments (E/W and
Width) inoperative. Occurs after a few years' service.

Replace capacitor C225 (22uF 50v 105 deg.C).

Symptom: Fluctuating brightness due to erratic screen
voltage in 8513 with serial number beginning 72-xxxx:

R477 (3.3M 1/4 watt) fails from high-voltage breakdown. Replace with
same value, 1/2 watt, or two 1.6M 1/4w in series. Resistor is located
between flyback transformer and aluminum heatsink of horizontal output
transistor. This model 8513 has only one control (focus) on its
flyback; the screen-voltage control is on the board attached to the
CRT socket.

I replace this resistor on general principle in aging monitors, and
readjust the screen voltage (variable resistor on CRT-socket circuit
board). These monitors usually also need their color balance
readjusted (controls labled R.BKG, G.BKG, B.BKG at rear of main board).

Symptom: No picture, no high voltage; pilot lamp on or
blinking:

Replace flyback transformer. We have had many flyback failures, and
have located a good source of replacements:

The horizontal-output transistor appears robust; we have never
replaced one, even after flyback transformer failure.

Symptom: One color absent or displayed improperly.

The large circuit board attached to the CRT socket contains the
cathode drivers for each color. The large output transistors and
their driver transistors often fail. Apply a test pattern (e.g.,
white-on-black text) and use an oscilloscope to compare the three
color channels, to locate the failed component(s).

Before we discovered the most common problems of 8512 and 8513 and
located a source of replacement flybacks, we had several repaired
(with good results) by:

EGA (5154) and PGA (5175) monitors are nearly identical except for the
video electronics contained in a metal box on the left side (when
facing the screen). Schematics ARE available from IBM, in _Technical
Reference, Options and Adapters, Volume 3_ of the "Personal Computer
Hardware Reference Library." Introduced in the mid 1980's, many 5154
and 5175 monitors are nearing the end of their service lifetimes,
i.e., tubes have dim picture and poor focus, and numerous capacitors'
values have decreased. In severe cases, we advise users to scrap the
monitors and convert to VGA.

The most common failure is in the power supply: Symptoms include
chirping noise, repetitive startup/shutdown (blinking LED pilot lamp)
or jagged edges on left and right of picture.

Replace three small electrolytic capacitors in the power supply:
C11 (47uF 40v), C13 (10uF 35v) and C14 (1uF 35v). These capacitors
fail from heat after long service.

The power-supply unit is removable. You must drill-out three pop-
rivets to open the metal box; replace them with sheet-metal screws.

My employer, an enormous state university, has found it very
economical to discontinue maintenance contracts on about eight hundred
IBM 3192 terminals and repair them in-house. 3192 repairs are
generally trivial, however, the assumed importance of the
administrative functions for which they are used makes it extremely
expedient to keep an adequate supply of spares available for instant
replacement.

The back cover of the monitor is held by two screws on the bottom and
two plastic spring-clips on the upper left and right sides (visible
with flashlight through rear ventilation slots). Use two L-shaped
tools (e.g., back-plates from IBM PC), inserted through upper
ventilation slots on the sides, to depress both clips simultaneously.
Then lift the cover off.

Symptom: No power, blown fuse.

The de-gaussing thermistor has probably shorted. This is the most
common failure we have encoutnered in 3192's. The thermistor is
identical to those used in 8512 and 8513; see above. Before replacing
fuse, use analog ohmmeter, or diode-test function on DVM, to check the
junctions of the two large power transistors in the power supply
section. Alternatively, measure resistance across the line-voltage
filter capacitor (C107) with power OFF and capacitor discharged. The
resistance should be greater than 500 ohms.

An intermittent "flutter" of the display can indicate incipient
failure of the de-gaussing thermistor; it is supposed to conduct
current through the de-gaussing coil for a few seconds during initial
power-on. Prior to failure, it may begin to conduct during normal
operation after warmup.

Symptom: No picture; repetitive clicking or beeping sound.

Bad part: High-voltage divider (the assembly between the flyback
transformer and the CRT anode), IBM part number 6405282 (about $20).

Replacement is easy: Unclip and unplug the ends going to CRT and
circuit-board. Pry the red plastic retaining ring out of the flyback
transformer; save it for the new divider assembly.

We have had difficulty obtaining voltage dividers from IBM;
an equivalent is available from Component Resource Corp (see address
above), same part number. Its red high-voltage wire is larger in
diameter than the original component: Use a 11/64" drill to enlarge
the hole in the red ferrule on the flyback; use a flat file to reduce
the bumps on the sides, and use a rat-tail file to make the split part
of the plastic thinner.

Voltage-divider failure causes additional damage in about 50% of
3192's:

[*] Newer models of 3192 are recognizable by a lighter shade of green
circuit board with a smaller parts count and natural-aluminum heat
sinks (instead of black anodized). The power-supply switching
transistor is 2SD1739 (ECG2324 equivalent) instead of 2SD1441. These
types are not interchangeable because 2SD1441 contains an internal
damper diode.

Symptom: Power supply dead, no pilot light.

Check diode D210. In the new model it is a plastic diode instead of
ceramic, and several have been found shorted. Other power supply
components (listed above) may also be damaged. D210 must be a fast-
recovery type diode.

Symptom: No vertical synch, horizontal line in center of
tube, possibly with deflection above or below line.

Bad part: Vertical amplifier (TDA2653A: large IC on heat sink).
Sometimes fails along with power supply, voltage divider and IC303, as
described above.

Symptom: No video but high voltage and sweep are present.

Check Q204 (npn), Q203 (pnp), or IC201 (7812; 20v in, 12v out). The
front-panel contrast pot controls Q404 which biases the video drivers
on the CRT board. Q204 and Q203 are powered by +12v from IC201.
Failure of any of those three devices will cut off video.

Most 3192's have proprietary-numbered integrated circuits. By
inspecting numerous units, we have compiled a list of industry-
standard numbers:

Connect terminal to the appropriate communications system and adjust
the picture as needed, before replacing the back cover. The upper
knob on the flyback transformer is CRT focus, the lower knob is screen
voltage (a.k.a. "sub-brightness").

Power switches commonly fail in 3192's. The switch (part number
8233403) is available from IBM. Since 3192's are rarely turned off,
it is practicable to remove a broken switch and solder wires between
the circuit-board pads in order to return a unit to service
temporarily if new switches are not in stock.